NASA's Mars Odyssey, which launched in 2001, broke the record Dec. 15, 2010 for longest-serving spacecraft at the Red Planet. The probe began its 3,340th day in Martian orbit at 5:55 p.m. PST (8:55 p.m. EST) on Wednesday to break the record set by NASA's Mars Global Surveyor, which orbited Mars from 1997 to 2006.
Source: ScienceDaily